Safety interlock switch



Oct. 20, 1953 D. sATlNoFF 2,656,425

SAFETY INTERLOCK SWITCH Filed may 14, 1951 INVENTOR.

BY Unep Nn AT ok/Y Patented Oct. 20, 1953 SAFETY INTERLOCK SWITCH DavidSatinoi, Utica, N. Y., assigner to the United States of America asrepresented by the Secretary of the United States Air Force ApplicationMay 14, 1951, Serial No. 226,259

(Granted Under Title 3'5, U. S. Code (1952),

Sec. 266) 6 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without payment to me of anyroyalty thereon.

This invention relates to electrical switching devices and particularlyto switches of the safety interlock type. In cabinets or otherenclosures for electrical equipment operating at dangerously highvoltages, such, for example, as radio transmitters, it is customary as asafety precaution to provide interlock switches on all doors for t'hepurpose of automatically deenergizing the equipment when a door isopened. Frequently switches of this type employ spring pressure to openthe switch. In such switches the contacts may freeze in their closedposition, due to corrosion or moisture and cold, causing the switch toremain closed when the door is opened and thus fail as a safety device.It is an object of this invention to provide a two-piece interlockswitch which can under no circumstances remain closed when the door isopened.

It is sometimes necessary to make tests or repairs on equipment when inan energized condition. In such cases the safety interlock is frequentlynullified by wedging the switch in a closed position or installing ajumper across the switch. The danger in this is that such makeshiftcheating devices may thoughtlessly be left 'in place thus defeating thepurpose of the safety interlock. It is accordingly another object ofthis invention to provide a two-piece safety interlock switch having abuilt-in cheater which can only be operated intentionally and which, ifoperated, is automatically rendered inoperative the next time the dooris closed.

The structural detail-s of an interlock switch incorporating the abovefeatures are shown in the accompanying drawings in which:

Fig. 1 shows a sectional plan view of the interlock switch in closedposition;

Fig. 2 shows a sectional elevation of the switch with plug andreceptacle parts of the switch separated;

Fig. 3 shows a sectional plan view of the receptacle part of the switchwith the cheater in operative position; and f Fig. 4 is an isometricview of the assembled switch. n

Referring to the drawings, the switch is composed of mating plug andreceptacle parts generally indicated by the numerals I and 2,respectively. The plug I has a body 3 of insulating material, and moldedtherein are two internally 2 connected contact prongs 5 and I. Ilheinsulating body of the plug is fastened to a metallic backing plate 1 byrivets 8 and 9.

The receptacle part 2 of the switch consists of a body of insulatingmaterial having upper and lower halves I0 and II fastened together andto a metallic angle plate I2 by rivets I3 and I4. The two halves I0 andII of the receptacle body may be, as in the embodiment shown, identicalmoldings having recesses therein to receive and position the conductorsI5 and I6 and the spring contacts I1I8 and I9--20 which are fastened tothe ends thereof by any suitable conductive fastenings such as spotwelds, etc. Terminals 2| and 22 are provided at the outer ends ofconductors I5 and I6 for connecting the switch into an electric circuit.

When the switch is in its closed position, as shown in Fig. 1, thecontacts 5 and 6 bridge the gap between contacts I'I and I 9 and therebycomplete a circuit between terminals 2I and 22. In the open position ofthe switch, shown in Fig. 2, the plug is removed from the receptacle andthe circuit between terminals 2I and 22 is broken. The plates 1 and I2provide means for mounting the switch. In a typical use of the switchthe receptacle part 2 would be mounted on the chassis of a cabinetenclosing electrical equipment while the plug part I would be mounted ona door to the cabinet. Since opening the doorremoves the plug part fromthe receptacle part of the switch, failure of the switch to operate whenthe door isopened is impossible.

In order to permit intentional completion of the circuit betweenterminals I and 2 when the plug and receptacle parts of the switch areseparated, the receptacle part has built into it what may be termed acheaten This device consists of a plunger 23 having a plate 24 attachedto its inner end and carrying connected spring contacts 25 and 26. Theplunger is positioned and guided at its outer end by a passageway 29formed in the two halves of the receptacle body, and at its inner end byplate 24 which engages and slides in slots 21 and 28 in the upper andlower halves I0 and II, respectively, of the receptacle body. The lengthof the plunger is sucfh that in its innermost position its outer endprotrudes a short way from the receptacle body as shown in Figs. 1 and2. 'Ihe plug is provided with a recess 30 to receive the protruding endof the plunger when the switch is in its closed position. In order tolatch the plunger 23 in its innermost position, which is the inoperativeposition of the cheaterf the plunger is provided with a notch 3| whichengages the edge of the opening in plate l2 through which the plunger 23passes. The spring finger 32 urges the plunger against this edge of theopening at all times causing the notch and edge to vbecome engaged whenthe two come into alignment.

When the switch is in the open position, the cheater may be operated bypressing the plunger against spring 32 to disengage the notch 3| andthen pulling the plunger all the way out to engage contacts 25-26 withcontacts Ill-2B, thus completing a circuit between terminals 2.1 and 22.The cheater may be manually V disengaged at any time by pushing theplunger all the way in so that the connection between vcontacts |8-20and 25-26 is broken and the shoulder of notch 3l drops in behind platel2 under the influence of spring 32. However, should `the "cheater beleft in its operative position, it will be automatically forced to itslatched inoperative 4position by the body 3 of plug .l the next .timethe interlock switch is closed. It will then remain in its inoperativeposition until intentionally .operated in the manner above described.Reopening of the interlock switch will not operate the ch eater even ifthe plunger should stick to or become frozen to the plug body 3, since.the restraining action of the shoulder of notch 31 against the plate l2would either cause the plunger to breakaway from the plug .or else causethe plunger itself to break.

l. ,A safety interlock switch having tivo separable mating parte, saidswitch being closed by joining said parts and opened .by separating saidparts, -Ineans attached to one of said parts and manually operable whensaid switch is open to form an electrical by-pass around said switch,and means attached to the other part of said switch and .cooperatingwith said manually op erable means when `said switch is closed to removesaid electrical by-pass.

.12. A safety interlock switch comprising separable mating plug andreceptacle parts, said receptacle part having a pair .of contacts and -apair of terminals connected to said contacts for connecting said .switchinto an electric circuit, said plug part having a pair of contactselectri cally connected together and positioned so as to enga-ge thecontacts of said receptacle part and t form an electrical connectionAtherebeween when the switch is in its closed position with plug andreceptacle parts joined, a second pair of contacts located in saidreceptacle part and connected to said terminals, a pair of electricallyconnected movable icontacts in said re ceptacle part, manual actuatingmeans for moving said pair of movable contacts between an in, operativeposition and an operative position, said pair of movable contacts insaid operative position engaging said second pair of contacts andforming an electrical Vconnection therehee tween, and means operated byclosing said switch to force said movable contacts from said operativeDOsition to said inoperative position.

3. A safety interlock switch comprising sepa-V rable mat-ing plug andreceptacle parts, a pair of terminals .associated with said receptaclepart for connecting said switch into an electrical circuit, said switchproviding a .connection between said terminals in its closed positionwhen said plug and receptacle parts are joined and an open circuitbetween said terminals in its open position when said plug andreceptacle parts are separated, an auxiliary switch in said receptaclepart for providing a connection between said terminals, a plungercoannect-exl to said auxiliary switch and protruding from said recep-`tacle part to permit manual operation of said auxiliary switch bypulling said plunger outward from said receptacle part, said plungerprotruding from said receptacle part at a point normally covered 'bysaid plug when said plug and receptacle `par-ts are joined, whereby, ifsaid auxiliary switch is in its operative position, the action ofv said.plug part against said plunger pushes .said auxiliary switch to aninoperative position during closure of said interlock switch.

A. A safety interlock switch for mounting on the door of a cabinetcontaining electrical equipment for the purpose of closing theenergizing circuit of said equipment when .said -door is closed andopening the energizing circuit of said equipment when said door isopened. ,an auxiliary switch in said interlock switch and connected inparallel thereto, means accessible when said door is Iopen for .manuallyclosing said auxiliary switch, and means on :said door cooperating withsaid manual closing means for opening said auxiliary switch when :saiddoor is closed.

y5. A safety interlock switch ,comprising .separable mating plug andlreceptacle parts; said receptacle part having two pairs of .separated`contacts connected in parallel between two external terminals forconnecting the switch into an electric circuit; said plug part having tapair of contacts electrically connected together and posi toned so as toengage one pair of contacts of said receptacle lpart and to form anelectrical connection therebetween when the switch is in its closedposition with plug and receptacle parts joined; a pair of electricallyconnected movable contacts in said receptacle part; plunger meansconnected to said movable contacts and, when said movable contacts arein an inoperative position, protruding a short way from said receptaclepart at a point normally covered by said plug part whensaid switch isclosed, whereby. when said switch is open, said movable con tacts may bebrought into an operative position References Cited in the le of thispatent UNITED STATES PATENTS Number Name yDate 1,414,421 Kries May 2,1922 2,231,737 Rutter -Feb. 1,1, 1941 2,348,197 Brongersma a May2, 19442,503,569 Verkuil Apr. 11,"1350 2,523,125 Ley Septr19, 1950

